Diamond diffractive optics—recent progress and perspectives
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-12-03 |
| Journal | Advanced Optical Technologies |
| Authors | Marcell Kiss, Sichen Mi, Gergely Huszka, Niels Quack |
| Institutions | École Polytechnique Fédérale de Lausanne |
| Citations | 13 |
| Analysis | Full AI Review Included |
Diamond Diffractive Optics: Technical Analysis and 6CCVD Solutions
Section titled “Diamond Diffractive Optics: Technical Analysis and 6CCVD Solutions”Executive Summary
Section titled “Executive Summary”This technical documentation analyzes the review by Kiss et al. on diamond diffractive optics, focusing on the material requirements and fabrication techniques that align directly with 6CCVD’s advanced MPCVD diamond capabilities.
- Material Superiority: Diamond (SCD/PCD) is confirmed as the optimal material for high-performance diffractive optical elements (DOEs) due to its extreme hardness (up to 110 GPa), high thermal conductivity (up to 2200 W/m K), and wide transparency window (0.22 µm to 20 µm).
- Precision Fabrication: The field is driven by micro- and nanofabrication techniques (E-beam lithography, RIE) enabling unprecedented dimensional control, necessary for high-efficiency DOEs operating from X-ray (30 nm features) to Far-IR wavelengths.
- Wavelength Dependence: Single Crystal Diamond (SCD) is the preferred substrate for short-wavelength (UV/Visible) and quantum applications (NV centers), while Polycrystalline Diamond (PCD) is suitable for longer wavelengths (IR) and large-area, high-power components.
- High Performance Demonstrated: Key achievements include High Contrast Gratings (HCGs) achieving 95.85% reflection at 1550 nm and high aspect ratio structures (up to 1:13.5) fabricated via optimized O2/Ar plasma RIE.
- 6CCVD Value Proposition: 6CCVD provides the necessary high-quality, large-area SCD and PCD substrates, coupled with precision polishing (Ra < 1 nm) and custom metalization, essential for replicating and advancing this state-of-the-art research.
Technical Specifications
Section titled “Technical Specifications”The following table summarizes critical material properties and performance metrics extracted from the research paper, highlighting the extreme capabilities of diamond DOEs.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Refractive Index | 2.3878 | N/A | SCD at 1550 nm |
| Thermal Conductivity (SCD) | 2200 | W/m K | Highest bulk value, critical for high-power lasers |
| Transparency Window | 0.22 - 20 | µm | Spanning UV to Far-IR |
| Hardness (SCD) | 50 - 110 | GPa | Extreme mechanical resistance |
| High Contrast Grating Reflection | 95.85 | % | Demonstrated at 1550 nm (Near-IR) |
| Maximum Etch Aspect Ratio | 1:13.5 | N/A | Achieved in PCD using Al resputtering RIE |
| Minimum Feature Size (Pitch) | 30 | nm | Demonstrated for X-ray gratings (E-beam lithography) |
| Sidewall Angle Control | 1.55 - 4.2 | ° | Achieved via optimized RIE processes |
| Polished Surface Roughness (SCD) | < 1 | nm | Required for low-loss UV/Visible optics |
| Laser Damage Threshold | 20× | N/A | Factor better than fused silica |
Key Methodologies
Section titled “Key Methodologies”The fabrication of high-performance diamond DOEs relies on advanced micro- and nanofabrication techniques, overcoming diamond’s extreme hardness and chemical inertness.
- Substrate Selection and Preparation:
- Growth: SCD or PCD substrates grown via Chemical Vapor Deposition (CVD).
- Polishing: Non-contact methods (e.g., Ion Beam Etching or RIE) are preferred over mechanical polishing to achieve sub-nanometer surface roughness (Ra < 1 nm) and minimize polishing pits, especially for UV/Visible optics.
- Patterning (Lithography):
- Nanoscale Features (< 1 µm): Electron Beam Lithography (EBL) is used for high-resolution structures (e.g., X-ray gratings, quantum photonics components).
- Microscale Features (> 1 µm): Photolithography (contact, DUV, Talbot) is used for longer wavelength DOEs (IR/Mid-IR).
- Hard Mask Implementation:
- Due to low selectivity between photoresist and diamond during RIE, a hard mask (e.g., SiO2, Al, Al2O3, Si, Cr, Ni) is deposited and patterned first.
- Metalization layers (e.g., Ti, Al) often serve a dual purpose: hard mask and conductive layer for EBL.
- Diamond Etching (Reactive Ion Etching - RIE):
- Chemistry: Primarily oxygen-based plasma (O2/Ar) is used to remove carbon atoms as COx byproducts. Chlorine or fluorine chemistries may be used for mask transfer.
- High Aspect Ratio Control: Techniques like periodic resputtering of the hard mask or continuous tuning of etch parameters are employed to achieve deep grooves (up to 13.7 µm) while maintaining near-vertical sidewalls (as low as 1.55° angle).
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the foundational materials and specialized processing required to replicate and advance the diffractive optics research detailed in this review. Our capabilities directly address the stringent requirements for material purity, dimensional control, and surface quality.
| Research Requirement (Kiss et al.) | 6CCVD Solution & Capability | Value Proposition for Engineers |
|---|---|---|
| High-Purity Single Crystal Diamond (SCD) | Optical Grade SCD Wafers (0.1 µm - 500 µm thickness) | Essential for low absorption in UV/Visible DOEs and for engineering high-coherence color centers (e.g., NV centers) in quantum applications. |
| Large-Area Substrates (PCD) | PCD Plates up to 125 mm Diameter | Enables industrial scaling of high-power laser optics (e.g., CO2 laser windows) and large-format spectrometers, surpassing the size limitations of traditional SCD. |
| Sub-nanometer Polishing | Precision Polishing Services (Ra < 1 nm for SCD; Ra < 5 nm for inch-size PCD) | Guarantees the ultra-smooth surfaces required to minimize scattering losses, critical for high-efficiency DOEs across all wavelengths. |
| Thick Substrates for X-ray/High Power | Substrates up to 10 mm Thickness | Provides the mechanical robustness and thermal mass necessary for high-energy X-ray gratings and high-power laser components. |
| Custom Hard Masks & Conductive Layers | In-House Custom Metalization (Au, Pt, Pd, Ti, W, Cu) | We supply diamond substrates pre-patterned with the necessary hard masks (e.g., Ti/Al) or conductive layers required for subsequent E-beam lithography and RIE processing. |
| Boron-Doped Diamond (BDD) | BDD Material (SCD or PCD) | Supports alternative fabrication routes, such as the selective graphitization via ion implantation demonstrated for X-ray gratings. |
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in MPCVD diamond growth and advanced material characterization. We offer expert consultation to assist researchers and engineers in selecting the optimal diamond grade (SCD vs. PCD), thickness, and surface preparation required for high-performance projects, including:
- High-Power Optics: Material selection to maximize thermal conductivity and Laser-Induced Damage Threshold (LIDT).
- Quantum Photonics: SCD substrates optimized for low nitrogen content and precise NV center creation.
- Micro/Nanofabrication: Guidance on hard mask compatibility and RIE recipe optimization based on specific DOE aspect ratio and sidewall angle requirements.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Diamond is an exceptional material that has recently seen a remarkable increase in interest in academic research and engineering since high-quality substrates became commercially available and affordable. Exploiting the high refractive index, hardness, laser-induced damage threshold, thermal conductivity and chemical resistance, an abundance of applications incorporating ever higher-performance diamond devices has seen steady growth. Among these, diffractive optical elements stand out—with progress in fabrication technologies, micro- and nanofabrication techniques have enabled the creation of gratings and diffractive optical elements with outstanding properties. Research activities in this field have further been spurred by the unique property of diamond to be able to host optically active atom scale defects in the crystal lattice. Such color centers allow generation and manipulation of individual photons, which has contributed to accelerated developments in engineering of novel quantum applications in diamond, with diffractive optical elements amidst critical components for larger-scale systems. This review collects recent examples of diffractive optical devices in diamond, and highlights the advances in manufacturing of such devices using micro- and nanofabrication techniques, in contrast to more traditional methods, and avenues to explore diamond diffractive optical elements for emerging and future applications are put in perspective.